System and method for frequency reuse for wireless point-to-point backhaul

ABSTRACT

A system and method for frequency reuse for wireless point-to-point backhaul. Frequency reuse is enabled through the cancellation of interfering signals generated by interference sources. In one embodiment, a conventional dish antenna is complemented with one or more additional auxiliary antennas (e.g., isotropic). The one or more additional auxiliary antennas enable cancellation of interfering signals whose direction of arrival (DOA) is off the dish antenna&#39;s bore-sight.

This application claims the benefit of and priority to provisionalapplication No. 61/978,376, filed Apr. 11, 2014, which is incorporatedherein by reference in its entirety.

BACKGROUND

1. Field

The present disclosure relates generally to microwave backhaularchitecture and, more particularly, to a system and method forfrequency reuse for wireless point-to-point backhaul.

2. Introduction

Conventional microwave backhaul architectures are generally implementedas either a split outdoor unit (split ODU) configuration or an alloutdoor unit (all ODU) configuration. Conventional split ODUconfigurations are generally comprised of both an indoor unit (IDU) andan outdoor unit (ODU), where the IDU and the ODU are connected over asingle channel coaxial interconnect. The IDU in a conventional split ODUconfiguration typically includes a modem, a digital-to-analog converterand a baseband-to-intermediate frequency converter.

Mobile backhaul providers are experiencing a growing demand forincreased capacity as well as a shift from voice services to dataservices. These factors are driving mobile backhaul networks towardshigh capacity IP/Ethernet connections. Additionally, the transition to4G and LTE networks is also driving the need for higher capacity, andmoving more packet traffic onto mobile backhaul networks.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features can be obtained, a more particular descriptionwill be rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments and are not therefore to be consideredlimiting of its scope, the disclosure describes and explains withadditional specificity and detail through the use of the accompanyingdrawings in which:

FIG. 1 illustrates a block diagram of a microwave backhaul systemaccording to an exemplary embodiment.

FIG. 2A illustrates a high-level block diagram of an IDU forimplementation within a microwave backhaul system according to anexemplary embodiment.

FIG. 2B illustrates a high-level block diagram of an ODU forimplementation within a microwave backhaul system according to anexemplary embodiment.

FIG. 3 illustrates an example backhaul scenario of a straight-line,multi-hop backhaul link.

FIG. 4 illustrates an example multi-hop backhaul link.

FIG. 5 illustrates an example of a directional dish antenna.

FIG. 6 illustrates an example backhaul link with two interferers.

FIG. 7 illustrates the performance in the example presence of twointerferers.

FIG. 8 illustrates an example of antenna response improvement.

FIG. 9 illustrates a flowchart of an example process.

DETAILED DESCRIPTION

Various embodiments are discussed in detail below. While specificimplementations are discussed, it should be understood that this is donefor illustration purposes only. A person skilled in the relevant artwill recognize that other components and configurations may be usedwithout parting from the spirit and scope of the present disclosure.

It is recognized that the microwave backhaul world is growing due toincreased bandwidth demands. FIG. 1 illustrates a block diagram of anexample microwave backhaul system 100 that includes IDU 102 and ODU 104.Microwave, as used throughout this disclosure, refers to bothterrestrial point-to-point (PtP) radio communications, as well aspoint-to-multipoint communications, and can include both wired and/orwireless communications.

Microwave backhaul system 100 initiates communication by accessing aninformation source, which can comprise, for example, audio data 106,video data 108, or any other data capable of being transmitted over anInternet Protocol (IP)/Ethernet connection 110. To facilitate thiscommunication, IDU 102 can be coupled to a core network. In particular,IDU 102 can be configured to acquire one or more sequences of digitaldata (e.g., audio data 106, video data 108, data transmitted overIP/Ethernet connection 110, or the like) from the core network. IDU 102can also be configured to support several additional services, such asEthernet, time-division multiplexing (TDM), and control data that isaggregated over a radio link.

IDU 102 can be implemented at a location that is substantially removedfrom ODU 104, such as at a location at ground level. For example, IDU102 can be positioned inside of a home or an office building, or otherstructure. Conversely, ODU 104 can be implemented at a substantiallyelevated location, such as on top of a pole, on top of an antenna tower,on top of a building, or other mounted location. In some embodiments,IDU 102 and ODU 104 can be separated by a significant distance (e.g., upto approximately 300 meters). In general, IDU 102 includes a modemassembly, while ODU 104 includes at least some RF functionalities aswell as corresponding digital capabilities.

IDU 102 and ODU 104 can be connected via communication pathway 112,which can be configured such that data can be transmitted between IDU102 and ODU 104. In various examples, communication pathway 112 cancomprise a twisted pair Ethernet cable, a fiber optic cable, a coaxialcable, an intermediate frequency (IF) cable, or any other cable suitablefor IDU-ODU communication. Therefore, depending on a chosencommunication medium, communication pathway 112 can facilitatetransmission of an analog signal or a digital signal between IDU 102 andODU 104. In some embodiments, communication pathway 112 can be awireless communication channel.

Antenna 116 can be coupled to ODU 104, and can be positioned close toODU 104. Therefore, microwave backhaul system 100 can be implementedsuch that data can be transmitted from IDU 102, across communicationpathway 112, to ODU 104, and subsequently to antenna 116 wherecommunication over a wireless link can then be initiated. Also,microwave backhaul system 100 can be implemented such that data receivedby antenna 116 can be transmitted from ODU 104 over communicationpathway 112 to IDU 102.

In one embodiment, ODU 104 can correct errors associated with a signalreceived over a wireless link via antenna 116. Microwave backhaul system100 can also be configured to support adaptive coding and modulation(ACM), which provides high reliability of microwave backhaul system 100even in extreme weather, such as wind, rain, hail, or other interferingenvironmental conditions. For example, ACM can adapt coding andmodulation rates to changing environmental conditions to therebyincrease throughput over a link and make efficient use of the existingspectrum. Thus, ACM enables the ODU to hitlessly manage the transitionswhen adjusting the number of transmission/receipt channels based on thechanges in the communication channel

FIGS. 2A and 2B illustrate high-level block diagrams of an example IDUand ODU, respectively, for use within a microwave backhaul systemaccording to an exemplary embodiment. IDU 202 and ODU 204 are coupledtogether via communication pathway 212. IDU 202 can represent anexemplary embodiment of IDU 102 of FIG. 1, and ODU 204 can represent anexemplary embodiment of ODU 104 of FIG. 1.

IDU 202 includes a power supply unit (PSU) 206, a CPU 208, a modemassembly 210, a digital-to-analog converter/analog-to-digital converter(DAC/ADC) block 216, a modulation block 218, and an intermediatefrequency (IF) module 220. In some embodiments, IDU 202 can also includean N-Plexer 222. CPU 208 is configured to carry out instructions toperform arithmetical, logical, and/or input/output (I/O) operations ofone or more of the aforementioned elements contained within IDU 202. Inan embodiment, CPU 208 can control operation of modulation block 218 andN-Plexer 222.

Modem assembly 210 is configured to perform modulation and demodulationof data that is to be transmitted between IDU 202 and ODU 204. In someembodiments, modem assembly 210 can function substantially similar to abaseband modem. Further, modem assembly 210 can be configured to cancelout noise associated with IDU 202 or communication pathway 212. DAC/ADCblock 216 can be configured to transmit and/or receive data from modemassembly 210. DAC/ADC block 216 is also configured to performdigital-to-analog and/or analog-to-digital conversions of data such thatthe data is suitable for transmission over communication pathway 212.

Modulation block 218 can also be configured to perform variousmodulation and/or demodulation techniques. In an embodiment, modulationblock 218 can be configured to perform amplitude-shift keying. Forexample, modulation block 218 can be configured to performamplitude-shift keying by utilizing a finite number of amplitudes, whereeach amplitude is assigned a unique pattern of binary digits. Eachpattern can then be configured to form the specific symbol that isrepresented by the particular amplitude. Additionally, when modulationblock 218 is configured to perform demodulation, modulation block 218determines the amplitude of the received signal and maps it back to thesymbol it represents, thus recovering the original data.

IF module 220 can be configured to transmit and/or receive data fromDAC/ADC block 216. IF module 220 is also configured to perform afrequency conversion of the received data such that data is suitable fortransmission over communication pathway 212. For example, IF module 220can be configured to convert data from a baseband frequency to an IF.

N-Plexer 222 can be configured to permit N-directional communicationover communication pathway 212. In particular, N-Plexer 222 isconfigured to isolate IDU 202 from ODU 204, while permitting them toshare a common antenna. N-Plexer 222 is also configured to receive acontrol signal (e.g. a Telemetry ASK signal) output from modulationblock 218, and to receive an IF signal output from IF module 220.Additionally, N-Plexer 222 can be configured to convert and/or combineeach of these inputs to form data. N-Plexer 222 is also configured totransmit and/or receive data, over communication pathway 212, betweenIDU 202 and ODU 204. In an embodiment, N-Plexer 222 can functionsubstantially as an analog duplexer (multiplexer/demultiplexer). In oneembodiment, communication pathway 212 can be embodied as one or more IFcables that can facilitate quadruple channel communication with one ormore IDUs.

In an exemplary embodiment, DAC/ADC block 216, modulation block 218, IFmodule 220 and N-Plexer 222 can be replaced by Digital N-Plexer 226. Inparticular, Digital N-Plexer 226 can be configured tomultiplex/demultiplex the required signal in the digital domain, ratherthan in the analog domain. Subsequently, Digital N-Plexer 226 can allowcommunication pathway 212 to be implemented as either a digital pathwayor an analog pathway. Using Digital N-Plexer 226 allows for a simplerimplementation of IDU 202. For example, when implementing IDU 202 havingDigital N-Plexer 226, no analog functionality would be required, andinstead only a single digital chip substrate would be needed. As aresult, the cost of implementing IDU 202 can be decreased. Additionally,using a Digital N-Plexer 226 can provide an improved yield, shorterproduction testing, lower assembly cost, lower peripheral componentcount, and can support greater distances between IDU 202 and ODU 204, toprovide some examples.

As illustrated in FIG. 2B, ODU 204 can also include an N-Plexer 228,which can be implemented in several different manners. For example,N-Plexer 228 can be an analog N-Plexer, a digital N-Plexer, or a splitfunction N-Plexer (e.g., where N-Plexer 228 is partially analog andpartially digital). When N-Plexer 228 represents a digital N-Plexer,N-Plexer 228 can function in a substantially similar manner as DigitalN-Plexer 226. In particular, N-Plexer 228 can be configured tomultiplex/demultiplex signals in the digital domain. N-Plexer 228 alsoallows for a simpler implementation of ODU 204 because no analogfunctionality would be required, and instead only a single digital chipsubstrate would need to be implemented within ODU 204. Therefore, thecost of implementing ODU 204 can also be decreased. Similar to DigitalN-Plexer 226, implementing N-Plexer 228 within ODU 204 can provide animproved yield, shorter production testing, lower assembly cost, lowerperipheral component count, and can support greater distances betweenIDU 202 and ODU 204, to provide some examples.

In an embodiment, IDU 202 and ODU 204 can be configured to perform anN-Plexer elimination technique. In particular, the functionalitydirected towards filtering RX, after being received over communicationpathway 212, and TX, before being transmitted over communication pathway212, can be removed from N-Plexers 226 and 228. Instead, thisfunctionality can be implemented within the digital chip substrate(e.g., integrated circuit) that comprises IDU 202 and the digital chipsubstrate (e.g., integrated circuit) that comprises ODU 204. IDU 202 andODU 204 can then filter the required signals through any combination ofan analog filtering process, a signal sampling process and/or a digitalfiltering process.

ODU 204 can also include CPU 230, ADC/DAC blocks 232 and 236, digitalsignal processor (DSP) 248, and RF module 234. CPU 230 can be configuredto function in a substantially similar manner as CPU 208. In particular,CPU 230 can be configured to carry out instructions to performarithmetical, logical, and/or I/O operations of one or more of theelements contained within ODU 204. In an embodiment, CPU 208 can controloperation of N-Plexer 228. ADC/DAC block 232 can be configured totransmit and/or receive data from N-Plexer 228. ADC/DAC blocks 232 and236 are also configured to perform analog-to-digital and/ordigital-to-analog conversions of data such that data can be properlytransmitted and/or received over communication pathway 212. Further, DSP248 can be configured to perform mathematical manipulation techniques ondata, such that data may be modified or improved according to a desiredprocessing method. For example, DSP 248 can be configured to measure,filter, or compress data prior to being output to ADC/DAC block 236,such that error detection and/or error correction can be performed onthe data. In an embodiment, after the data is received, overcommunication pathway 212, at ODU 204, the data traverses throughN-Plexer 228, to ADC/DAC block 232, to DSP 248, to ADC/DAC block 236, toRF module 234 and to antenna 244 before being transmitted acrosswireless link 246. Similarly, after data is received over wireless link246, at ODU 204, data traverses from antenna 244 to RF module 234, toADC/DAC block 236, to DSP 248, to ADC/DAC block 232, and to N-Plexer 228before being transmitted over communication pathway 212. As will bedescribed in greater detail below, DSP 248 can also be configured toremove the effect of interference signals from one or more interferingsources that are present in the received signals output by antenna 244.

RF module 234 can be configured to transmit and/or receive data fromADC/DAC block 236. RF module 234 can also be configured to perform afrequency conversion of data such that data can be properly receivedover communication pathway 212. For example, when data is received at RFmodule 234, data can have a frequency residing in the IF range.Therefore, RF module 234 can up-convert data from an IF to a RF suchthat data can then be transmitted over wireless link 246. RF module 234can also be configured to down-convert a signal received over thewireless link from a RF to an IF such that the received signal can betransmitted over communication pathway 212 to IDU 202.

The deployment process of backhaul links by operators is typicallygoverned by the state regulator, often obligating the operators toacquire several frequency bands to guarantee interference-free operationof the multiple backhaul links. In the present disclosure, it isrecognized that reducing the associated cost of holding multiplefrequency bands to cover a certain region is desirable.

Typically, a straight-line, multi-hop backhaul link includes no morethan 2-3 hops, before the straight line breaks. FIG. 3 illustrates anexample backhaul scenario of a straight-line, multi-hop backhaul link.As illustrated, such a link includes three hops, wherein each of thehops uses a different frequency band f_(c1), f_(c2), f_(c3) to assure nointer-hop interference.

In the present disclosure, a solution is presented that enables reuse ofthe same single channel over and over in a plurality of backhaul linksin the network. Frequency reuse is enabled through the cancellation ofinterfering signals generated by interference sources. In oneembodiment, a conventional dish antenna is complemented with one or moreadditional auxiliary antennas (e.g., isotropic). Here, the one or moreadditional auxiliary antennas enable cancellation of interfering signalswhose direction of arrival (DOA) is off the dish antenna's bore-sight.

The dish antenna output signal includes the highly-amplified desiredsignal summed with an undesired interference signal arriving offbore-sight but with a lower gain (e.g., −35 dBc) compared to the desiredsignal. This is due to the side-lobes gain of the dish antenna. In theexample, this results with a limiting SNR of 35 dB. To avoid thisinterference in microwave backhaul links, regulators typically obligateuse of different frequency bands, thereby driving up costs for theoperators.

An auxiliary omni-directional antenna output signal includes an equalgain summation of the desired signal and the interference signal. In thepresent disclosure, it is recognized that by pre-adjusting the gain ofthis signal followed by a subtraction from the dish antenna's output,the interference signal is cancelled with a small gain penalty in thedesired signal. In general, output signals are down-converted tobaseband such that a digital circuit is then able to remove theinterfering signals and extract only the desired signal.

To illustrate this concept, reference is made to the example multi-hopbackhaul link illustrated in FIG. 4. As illustrated, the interferingsignal's DOA into Hop 2's receive antenna is at an angle α off thebore-sight. The dish antenna has a radiation pattern denoted as U_(d)(θ)and the isotropic antenna radiation pattern is denoted by U_(i)(θ). Bydefinition, the omni-directional nature of the isotropic antennadictates that the isotropic antenna radiation pattern is a constant forall angles (at least in 2D). The dish antenna, on the other hand, has aradiation pattern that is angle-selective. In other words, there is highgain in the narrow few degrees of the bore-sight beam, with significantbut not satisfactory side-lobes response. FIG. 5 illustrates an exampleperformance of a directional dish antenna.

To illustrate an interference cancellation mechanism that enablesfrequency reuse, reference is now made to FIG. 6, which illustrates anexample backhaul link with two interferers. In this example, the antennaconfiguration again includes a parabolic dish antenna complemented byone isotropic antenna. The output of the parabolic dish antenna isy_(d), while the output of the isotropic antenna is y_(i). Here, itshould be noted that more than one isotropic antenna can be used indifferent embodiments to address one or more interference sources thatcan exist in a given installation scenario.

In the example of FIG. 6, the received signals at the parabolic dishantenna and the isotropic antenna can be described as follows:

$\underset{\_}{y} = {\begin{bmatrix}y_{d} \\y_{i}\end{bmatrix} = {{{\begin{bmatrix}{{G_{d}\left( \alpha_{1} \right)}A} & {{G_{d}\left( \alpha_{2} \right)}A} & {G_{d}(0)} \\{{G_{i}\left( \alpha_{1} \right)}A} & {{G_{i}\left( \alpha_{2} \right)}A} & {G_{i}(0)}\end{bmatrix}\begin{bmatrix}x_{11} \\x_{12} \\x_{2}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2}\end{bmatrix}}\overset{\bigtriangleup}{=}{{H \cdot \underset{\_}{x}} + \underset{\_}{n}}}}$where x₁₁, x₁₂, and x₂ are the independent transmitted signals over Hop11, Hop 12, and Hop 2, respectively, n₁, n₂ are the independent additivewhite Gaussian noise (AWGN) at the respective antennas, and His thechannel describing this system. 20 log₁₀A [dB] is the interferers powerabove the desired signal (e.g., 20 log₁₀A=30 dBc), i.e., bothinterferers transmit power is the same.

${{E{n_{1,2}}^{2}} = \sigma^{2}},{{E{x_{1,2}}^{2}} = 1},{{SNR}_{planned} = \frac{1 \cdot \left( {G_{d}(0)} \right)^{2}}{\sigma^{2}}}$is the planned link SNR in the desired link (e.g., 40 dB) if nointerferers were present (i.e., no frequency reuse). 20 log₁₀G_(d)(0)[dBi] is the dish antenna gain at bore-sight (e.g., 43.6 dBi for atypical microwave antenna). 20 log₁₀G_(d)(α) [dBi] is the dish antennagain at DOA α. 20 log₁₀G_(i)(0) [dBi] is the isotropic antenna gain atbore-sight. 20 log₁₀G_(i)(α_(1,2)) [dBi] is the isotropic antenna gainat DOA α_(1,2). If the interferer transmitters (x₁₁, x₁₂) are located atthe same height of the desired signal transmitter (x₂) then the lattertwo terms (20 log₁₀G_(i)(0) and 20 log₁₀G_(i)(α_(1,2))) are of equalgain value, since the omni-directional antenna has an equal gain overhorizontal rotation.

The appropriate Linear Minimum Mean Square Equalizer (LMMSE) solutionthat can be determined by the signal processing module is then:

$\underset{\_}{\hat{x}} = {{{H^{\prime}\left( {{HH}^{\prime} + {\sigma^{2}I}} \right)}^{\prime} \cdot \underset{\_}{y}}\overset{\bigtriangleup}{=}{{C \cdot \underset{\_}{y}} = {{C \cdot \left( {{H\underset{\_}{x}} + \underset{\_}{n}} \right)} = {{{CH}\underset{\_}{x}} + {C\underset{\_}{n}}}}}}$

In one example, the signal processing module is embodied as DSP 248. TheLMMSE solution can be described as a fixed solution as it can be assumedthat the channel H is known. In another embodiment, the signalprocessing module H is unknown and can be estimated. For example, aLeast Mean Square (LMS) solution can provide an adaptive way ofimplementing LMMSE by estimating H. Here, the LMS solution would attemptto minimize error over time by updating and improving the estimation ofH, and hence C. Note that in other embodiments, other solutions can bebased on Minimum Mean Square Equalizer or Maximum Likelihood.

Further note that out of the two forms of the LMMSE solutions (both areidentical as long as σ²≠0):H⁺(HH⁺+σ²I)⁻¹ and (H⁺H+σ²I)⁻¹H⁺

In one embodiment, the chosen one is the former one, which achievesbetter numerical accuracy for under-determinant systems (and especiallyfor high planned SNR), that is too few measurements in conjunction withtoo much signals—as is the case here. And specifically for the desiredsignal:

${\hat{x}}_{2} = {\overset{\overset{signal}{︷}}{({CH})_{({3,3})}x_{2}} + \overset{\overset{{res}.\mspace{11mu}{interferences}}{︷}}{{({CH})_{({3,1})}x_{11}} + {({CH})_{({3,2})}x_{12}}} + \overset{\overset{noise}{︷}}{{(C)_{({3,1})}n_{1}} + {(C)_{({3,2})}n_{2}}}}$Therefore the resultant SINR is:

${SINR}_{{dish} + {isotropic}} = \frac{{({CH})_{({3,3})}}^{2} \cdot 1}{{{({CH})_{({3,1})}}^{2} \cdot 1} + {{({CH})_{({3,2})}}^{2} \cdot 1} + {\sigma^{2}\left\lbrack {{(C)_{({3,1})}}^{2} + {(C)_{({3,2})}}^{2}} \right\rbrack}}$

If the isotropic (omni-directional) antenna is not used then only thedish antenna's output is available:

$y_{d} = {{{\begin{bmatrix}{{G_{d}\left( \alpha_{1} \right)} \cdot A} & {{G_{d}\left( \alpha_{2} \right)} \cdot A} & {G_{d}(0)}\end{bmatrix}\begin{bmatrix}x_{11} \\x_{12} \\x_{2}\end{bmatrix}} + n_{1}} = {{{G_{d}(0)}x_{2}} + {{G_{d}\left( \alpha_{1} \right)} \cdot {Ax}_{11}} + {{G_{d}\left( \alpha_{2} \right)} \cdot {Ax}_{12}} + n_{1}}}$The LMMSE solution for this case, C, is a multiplying scalar and as suchit preserves the SINR at its input (output SINR equals to input SINR).

${SINR}_{{dish}.{only}} = {{\frac{C^{2}}{C^{2}}\frac{\left( {G_{d}(0)} \right)^{2}}{\left( {{G_{d}\left( \alpha_{1} \right)} \cdot A} \right)^{2} + \left( {{G_{d}\left( \alpha_{2} \right)} \cdot A} \right)^{2} + \sigma^{2}}} = \frac{\left( {G_{d}(0)} \right)^{2}}{\left( {{G_{d}\left( \alpha_{1} \right)} \cdot A} \right)^{2} + \left( {{G_{d}\left( \alpha_{2} \right)} \cdot A} \right)^{2} + \sigma^{2}}}$Again the SNR gain will actually be a negative number (i.e., it will bea penalty) is:

${SNRGain}_{{dish} + {isotropic}} = \frac{{SNR}_{{dish} + {isotropic}}}{{SNR}_{planned}}$${SNRGain}_{{dish}.{only}} = \frac{{SINR}_{{dish} + {isotropic}}}{{SNR}_{planned}}$

The performance in the example presence of two interferers can bedepicted as shown in FIG. 7. As illustrated in the example of FIG. 7only when both interferers are roughly at the same DOA of X (e.g., ˜45)or alternatively one interferer is at X° and the other one is at mirrorangle (−X°) then the performance loss, in the case of isotropic assistedcancellation, can be limited to less than 3 dB and it could even reach0.3 dB. Therefore the cancellation coverage is significantly narroweddown to ±45+(−13.8°) such that loss is less than 3 dB.

The output of the equalizer, specifically for the desired signal x₂ willhave a significantly improved SNR compared to the case where noauxiliary antenna(s) were used and the dish antenna operated on its own.It can be shown that the overall system of the dish antenna plus one ormore auxiliary antennas plus digital baseband processing is equivalentto a significantly (more than 30 dB lower side-lobes) improved (muchnarrower) single dish antenna response as shown in FIG. 8.

The implication of this solution is that the link-planned SNR can bepreserved even in the presence of co-channel strong interferers. Thisenables operators to significantly reduce spectrum holding yearly feesby sufficing with holding only a single frequency band. It also easesthe network frequency planning because such a system is significantlyrobust of interferers. The number of auxiliary antennas and their type(directional, omni-directional, etc.) is a design parameter and can betraded off at the expense of performance preservation in the main link.

Having described an equalizer system that complements a parabolic dishantenna with one or more auxiliary antennas, reference is now made tothe flowchart of FIG. 9, which illustrates an example process. Asillustrated, the process can begin at step 902 where a signal processingmodule receives first signals based on an output of a parabolic dishantenna. Next, at step 904, the signal processing module receives secondsignals based on output(s) from one or more auxiliary antennas (e.g.,isotropic).

The first signals include a desired signal along with interferencegenerated by one or more interference sources transmitting in the samefrequency band as the desired source. In one example, the one or moreinterference signals are received by the parabolic dish antenna at a DOAthat is off the dish antenna's bore-sight and at a lower gain. Incontrast, the one or more auxiliary antennas output signal can includean equal gain summation of the desired signal and the interferencesignal.

At step 906, the signal processing module can then be configured toremove interference from one or more interfering sources n the firstsignals using the second signals. The cancellation of the interferencesignals can be performed with a small gain penalty in the desired signalfrom the desired source. As a result, the relative interference of theone or more interference sources is reduced, thereby enabling greateropportunities for frequency reuse.

A solution has been described based on the example of two interferersand one auxiliary antenna. This example is not intended to be limitingto the scope of the present disclosure. The solution outlined above canbe generalized to extend to different numbers of interferers and adifferent number of auxiliary antennas as would be appreciated.

Another embodiment of the present disclosure can provide a machineand/or computer readable storage and/or medium, having stored thereon, amachine code and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein.

Those of skill in the relevant art would appreciate that the variousillustrative blocks, modules, elements, components, and methodsdescribed herein may be implemented as electronic hardware, computersoftware, or combinations of both. To illustrate this interchangeabilityof hardware and software, various illustrative blocks, modules,elements, components, methods, and algorithms have been described abovegenerally in terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system. Thoseof skill in the relevant art can implement the described functionalityin varying ways for each particular application. Various components andblocks may be arranged differently (e.g., arranged in a different order,or partitioned in a different way) all without departing from the scopeof the subject technology.

These and other aspects of the present disclosure will become apparentto those skilled in the relevant art by a review of the precedingdetailed disclosure. Although a number of salient features of thepresent disclosure have been described above, the principles in thepresent disclosure are capable of other embodiments and of beingpracticed and carried out in various ways that would be apparent to oneof skill in the relevant art after reading the present disclosure,therefore the above disclosure should not be considered to be exclusiveof these other embodiments. Also, it is to be understood that thephraseology and terminology employed herein are for the purposes ofdescription and should not be regarded as limiting.

What is claimed is:
 1. A microwave receiver system, comprising: aparabolic dish antenna that is configured to receive microwave signalstransmitted via a plurality of backhaul links, wherein the plurality ofbackhaul links comprises at least a first link and a second link,wherein a first node is configured to transmit a first signal to asecond node via the first link using a first frequency band, and asecond node is configured to transmit a desired signal to the parabolicdish antenna via the second link using the first frequency band, whereinthe first node further comprises an interference source by transmittingan interference signal in the first frequency band comprising at least aportion of the first signal directly to the parabolic dish antenna, theparabolic dish antenna further configured to generate a dish antennaoutput according to the desired signal and the interference signalreceived by the parabolic dish antenna; one or more auxiliary antennasthat are configured to receive microwave signals comprising a version ofthe desired signal from the second node and a version of theinterference signal directly from the first node, and generate one ormore auxiliary antenna outputs according to the version of the desiredsignal and the version of the interference signal received by the one ormore auxiliary antennas; and a signal processing module that isconfigured to receive first signals based on the dish antenna output andsecond signals based on the one or more auxiliary antenna outputs, theprocessing module further configured to use the one or more auxiliaryantenna outputs to remove interference from the interference source thatare present in the first signals based on the dish antenna output. 2.The microwave receiver system of claim 1, further comprising an RFmodule that down-converts the dish antenna output.
 3. The microwavereceiver system of claim 1, wherein the one or more auxiliary antennasare isotropic antennas.
 4. The microwave receiver system of claim 1,wherein the one or more auxiliary antennas comprise a single auxiliaryantenna.
 5. The microwave receiver system of claim 1, wherein the one ormore auxiliary antennas comprise a plurality of auxiliary antennas. 6.The microwave receiver system of claim 1, wherein the signal processingmodule uses a Linear Minimum Mean Square Equalizer technique to removethe interference signal.
 7. The microwave receiver system of claim 1,wherein the signal processing module uses a Minimum Mean SquareEqualizer technique to remove the interference signal.
 8. The microwavereceiver system of claim 1, wherein the signal processing module uses aMaximum Likelihood technique to remove the interference signal.
 9. Amethod, comprising: generating a dish antenna output from a parabolicdish antenna that is configured to receive microwave signals transmittedvia a plurality of backhaul links, wherein the plurality of backhaullinks comprises at least a first link and a second link, wherein a firstnode is configured to transmit a first signal to a second node via thefirst link using a first frequency band, and a second node is configuredto transmit a desired signal to the parabolic dish antenna via thesecond link using the first frequency band, wherein the first nodefurther comprises an interference source by transmitting an interferencesignal in the first frequency band comprising at least a portion of thefirst signal directly to the parabolic dish antenna, the parabolic dishantenna further configured to generate the dish antenna output accordingto the desired signal and the interference signal received by theparabolic dish antenna; generating one or more auxiliary antenna outputsfrom one or more auxiliary antennas that are configured to receivemicrowave signals, the microwave signals comprising a version of thedesired signal from the second node and a version of the interferencesignal directly from the first node, the one or more auxiliary antennaoutputs generated according to the version of the desired signal and theversion of the interference signal received by the one or more auxiliaryantennas; and removing, using a signal processing module configured toreceive first signals based on the dish antenna output and secondsignals based on the one or more auxiliary antenna outputs, interferencefrom the interference source that are present in the first signals,wherein the one or more interference sources transmit in the samefrequency band as the desired source.
 10. The method of claim 9, furthercomprising down-converting the dish antenna output using an RF module.11. The method of claim 9, wherein the one or more auxiliary antennasare isotropic antennas.
 12. The method of claim 9, wherein the one ormore auxiliary antennas comprise a single auxiliary antenna.
 13. Themethod of claim 9, wherein the one or more auxiliary antennas comprise aplurality of auxiliary antennas.
 14. The method of claim 9, wherein theremoving comprises removing using a Linear Minimum Mean Square Equalizertechnique.
 15. The method of claim 9, wherein the removing comprisesremoving using a Minimum Mean Square Equalizer technique to remove theinterference signal.
 16. The method of claim 9, wherein the removingcomprises removing using a Maximum Likelihood technique to remove theinterference signal.
 17. A method, comprising: receiving, by a signalprocessing module, first signals based on an output of a parabolic dishantenna that is configured to receive microwave signals from a desiredsource, the first signals transmitted via a plurality of backhaul links,wherein the plurality of backhaul links comprises at least a first linkand a second link, wherein a first node is configured to transmit afirst signal to a second node via the first link using a first frequencyband, and a second node is configured to transmit a desired signal tothe parabolic dish antenna via the second link using the first frequencyband, wherein the first node further comprises an interference source bytransmitting an interference signal in the first frequency bandcomprising at least a portion of the first signal directly to theparabolic dish antenna, the parabolic dish antenna further configured togenerate the dish antenna output according to the desired signal and theinterference signal received by the parabolic dish antenna; receiving,by the signal processing module, second signals based on an output ofone or more auxiliary antennas, the second signals comprising a versionof the desired signal from the second node and a version of theinterference signal directly from the first node, the output of the oneor more auxiliary antenna generated according to the version of thedesired signal and the version of the interference signal received bythe one or more auxiliary antennas; and removing, using the signalprocessing module, configured to receive first signals based on the dishantenna output and second signals based on the one or more auxiliaryantenna outputs, interference from the interference source that arepresent in the first signals, wherein the one or more interferencesources transmit in the same frequency band as the desired source. 18.The method of claim 17, wherein the one or more auxiliary antennas areisotropic antennas.
 19. The method of claim 17, wherein the one or moreauxiliary antennas comprise a single auxiliary antenna.
 20. The methodof claim 17, wherein the one or more auxiliary antennas comprise aplurality of auxiliary antennas.